The present invention relates to a monolithic metallic honeycomb body with a varying number of channels, which is preferably used as a catalyst carrier body for the catalytic conversion of exhaust emissions from internal combustion engines. The invention also relates to a method for manufacturing the honeycomb body.
Such honeycomb bodies are known in a large number of configurations as is disclosed, for example, by European Patent 0 245 737 B1, corresponding to U.S. Pat. Nos. 4,832,998; 4,803,189; 4,946,822; and 4,923,109 and European Patent 0 430 945 B1, corresponding to U.S. Pat. Nos. 5,139,844; 5,105,539; and 5,135,794.
It is also known that for the most efficient exhaust emission control it may be advisable to place a plurality of sheet metal layers, possibly having a differing honeycomb structure or honeycomb size, in series in the direction of flow. However, such a body is no longer monolithic. As a result, higher costs are incurred in the manufacture, incorporation into a casing pipe and possibly also in the coating of the honeycomb body. The creation of additional internal flow edges for metal honeycomb bodies by turning over partial areas of corrugation crests or corrugation troughs is therefore also disclosed, for example, by European Patent 0 484 364 B1. Although, with respect to the internal flow distribution of the honeycomb body, that achieves an effect similar to that of sheet metal layers having differing channel sizes disposed in series, the catalytically active surface which is available remains the same. Therefore, all of the advantages of sheet metal layers with differing channel sizes disposed in series cannot actually be obtained thereby.
U.S. Pat. No. 5,549,873 also discloses a monolithic honeycomb body, in which a leading area has a smaller number of channels and a lower heat capacity than remaining area due to cut-outs in the sheet metal layers.
In order to refer to a honeycomb body as a monolithic body it must have an internal cohesion. European Patent 0 542 775 B1, corresponding to U.S. Pat. No. 5,328,774, has already disclosed a monolithic honeycomb body, in which the internal cohesion is achieved through the use of sheet metal layers, which are smooth or slightly structured relative to the dimensions of the channels. That is accomplished in such a way that a part of the sheet metal layers in the honeycomb body extends continuously from the inlet flow end to the outlet flow end. The honeycomb body has different numbers of sheet metal layers and channels per cross-sectional area. In other words, channels of differing size, in different succeeding sections, are provided in the direction of flow. In a honeycomb body disclosed by European Patent 0 543 775 B1, the desired variation in the number of channels and therefore in the catalytically active surface areas is achieved in such a way that the monolithic honeycomb body is constructed from sheet metal layers having different widths and differently dimensioned structures. The present invention proceeds from that state of the art.
The manufacture of such a honeycomb body is relatively expensive, since a plurality of differently structured sheet metal layers have to be layered on top of and along side one another. Handling such a layered stack is comparatively difficult, especially when the stack with both of its ends is to be coiled around a minimum of two fixed points.
It is accordingly an object of the invention to provide a monolithic metallic honeycomb body with a varying number of channels and a method for manufacturing the honeycomb body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which the honeycomb body is easier to manufacture with a varying number of channels and possibly a heat capacity varying from section to section as well.
With the objects of the invention in view there is provided, in accordance with the invention, a monolithic honeycomb body, comprising mutually spaced-apart inlet and outlet flow ends; different successive sections between the flow ends; at least partially structured sheet metal layers having structures forming walls defining channels through which a fluid can flow in one flow direction; the channels having sizes or numbers varying in the different successive sections in the flow direction; at least a part of the structured sheet metal layers extending from the inlet flow end to the outlet flow end, for achieving an internal cohesion of the body; each of the sheet metal layers having at least a first structure and a second structure with different dimensions; and at least one of the structures extending over only one of the sections.
In contrast to the known monolithic honeycomb body, the internal cohesion is not (solely) achieved by sheet metal layers which are smooth or slightly structured relative to the dimension of the channels, but (also) by the structured sheet metal layers having structures which form channels in the flow direction. This reinforces the cohesion of the body and/or simplifies the manufacture, because there are fewer individual structured sheet metal strips to be handled.
In accordance with another feature of the invention, there are provided sheet metal layers which are smooth or slightly structured relative to the dimensions of the channels and are disposed between the structured sheet metal layers. The sheet metal layers that are smooth or slightly structured relative to the dimensions of the channels extend over at least one section of the honeycomb body. Smooth sheet metal layers, which extend over the entire length of the honeycomb body, may also be provided. These sheet metal layers which are smooth or slightly structured relative to the dimensions of the channels lend the honeycomb body additional internal support, thereby further reinforcing the monolithic characteristic of the honeycomb body.
In accordance with a further feature of the invention, there are provided further structured sheet metal layers, which extend over at least one section of the honeycomb body. Such a honeycomb body is consequently constructed from sheet metal layers with differing widths and structures having differing dimensions, thereby achieving a variation in the number of channels and therefore also in the catalytically active surface areas. The additional structured sheet metal layers are preferably disposed between the sheet metal layers extending from the inlet flow end to the outlet flow end. They occupy the intervals between the latter sheet metal layers.
In accordance with an added feature of the invention, the additional structured sheet metal layers are disposed in such a way that the honeycomb body has a constant cross-section in the direction of flow. Such a honeycomb body requires a casing having a simple construction, which in the case of a honeycomb body with a circular cross section may be a tubular construction.
In accordance with an additional feature of the invention, each structured sheet metal layer extending right through the entire body has structures which are constructed symmetrically relative to a common plane. A honeycomb body constructed from sheet metal layers which have such a structure is easier to handle, since there is no need to consider its orientation.
In accordance with yet another feature of the invention, the structured sheet metal layers passing right through the entire body have physical dividing lines, formed at an interval from one another and running between adjacent structures having different dimensions substantially transversely to the direction of flow. The advantage of such sheet metal layers resides in the fact that between the adjacent structures having different dimensions there is an abrupt transition between the structures. The straight-line length of the structures having different dimensions is equal to the length of the physical dividing line. The structures may have different heights or shapes.
In accordance with yet a further feature of the invention, the connection between the adjacent structures having different dimensions is maintained through the sections between the physical dividing lines. The section between two adjacent dividing lines lies at least partially on a common side of the adjacent structure. The structures may have an undulating or meandering form, for example. In the case of a meandering structure, the section may extend over the entire common side of the adjacent structures. If the structures are constructed with an undulating form having differing amplitudes, the adjacent structures preferably have sides with an equal gradient. The sections between two physical dividing lines then lie on the common sides.
In accordance with yet an added feature of the invention, instead of common sides, the adjacent structures may also have common crests and/or troughs.
Configurations of a honeycomb body are known, which can be constructed from a plurality of individual sheet metal layers. Configurations are also known in which the entire honeycomb body includes just one or two spirally wound or meandering sheet metal layers. The term intertwined is used herein as a generic term and it is of no importance whether the individual sheet metal layers are wound or folded. The invention may also be used for configurations in which the structured sheet metal layers are not separated by smooth sheet metal layers, but instead have adjacent structured sheet metal layers with structures running at an angle to one another.
For many applications it is advisable for a honeycomb body to have a greater heat capacity internally than in its inlet end area. Where the honeycomb body is used as catalyst carrier in the exhaust system of an internal combustion engine this feature enhances the characteristics when restarting the engine after interrupted running. In the case of diesel engines and lean-burn engines, for example, it permits continuous catalytic conversion even under heavily fluctuating operating conditions with phases in which relatively cold exhaust emissions reach the catalytic converter. In the case of the present invention, the heat capacity is influenced by the thickness of the sheet metal layers, so that the additional sheet metal layers can be made at least partially thicker in selected areas in order to increase the heat capacity in these selected areas.
With the objects of the invention in view, there is additionally provided a method for manufacturing a monolithic honeycomb body, which comprises forming structures in at least one sheet metal layer; intertwining the at least one sheet metal layer to form a honeycomb body with walls formed by the structures defining channels through which a fluid can flow in one flow direction; and before or during the forming of the structures, forming mutually spaced apart physical dividing lines in each of the sheet metal layers along a common imaginary line running substantially transversely to the flow direction, and forming the structures with different dimensions, especially different structural heights, on both sides of the dividing lines. The differing structures may be formed successively or simultaneously.
In accordance with another mode of the invention, the dividing line is incorporated into the sheet metal layer by cutting. The cutting process as such may be performed through the use of a cutter, preferably a rotary cutter. According to a further proposal the physical dividing line is formed into the sheet metal layer through the use of a laser cutting process.
In accordance with a concomitant mode of the invention, the dividing line and the structures are formed simultaneously, by running a sheet metal strip through two different corrugated rollers situated side by side on a common axis.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a monolithic metallic honeycomb body with a varying number of channels and a method for manufacturing the honeycomb body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.